Classification of hypertension in pregnancy

In many ways there should be no need to classify hypertensive disorders in clinical practice. The very presence of rising blood pressure should alert the clinician to seek evidence for the development of pre-eclampsia and whether there are any emerging abnormalities of fetal growth and/or maternal renal, cerebral, hepatic or coagulation functions which may necessitate specific treatment, including delivery. While such a view may be appropriate for experienced clinicians with an understanding of the pathophysiology of the hypertensive disorders of pregnancy, it is of little help to junior or less experienced medical staff. Moreover, without an agreed international classification system it is impossible to compare truly clinical outcome, intervention or basic research studies from different units; as entry criteria to these studies may differ considerably across individual units and certainly across countries. In this chapter we highlight the limitations of the existing classification systems and propose a system that is based on our present understanding of the pathophysiology of pre-eclampsia. The proposed system is not a radical departure from previous classifications, with grouping of hypertensive subjects into gestational hypertension, pre-eclampsia and chronic (usually essential) hypertension. Proteinuria, while remaining a hallmark of pre-eclampsia, is no longer considered a 'sine qua non' for this disorder to be diagnosed, reflecting our greater understanding of the maternal and fetal abnormalities in preeclampsia since previous classification systems were developed. This classification system has been compared with the traditional system of diagnosing proteinuric pre-eclampsia in a study of 1183 women with hypertension in pregnancy: diagnosing pre-eclampsia in this new manner still stratifies a high-risk group of pregnant women and the proposed diagnosis of gestational hypertension in this system stratifies a group of women at low maternal and fetal risk, provided that continual maternal and fetal monitoring is employed. We hope that this system of classification can be adopted uniformly, permitting appropriate triage of pregnant women into higher and lower clinical risk groups while allowing us to compare 'apples with apples' in future research studies.